Williamson headed north earlier this week with New Zealand Trotting Free-For-All fourth-placegetter Majestic Man and Dominion third-placegetter Monty Python.
The group race performers will arrive today at Tony Herlihy's Papakura stable, where they will be based alongside the Williamson-owned Kenny's Dream.
Kenny's Dream, who moved north to Herlihy's stable from Williamson's barn over winter, is also a confirmed starter in the Interdominions.
Majestic Man and Monty Python both headed north feeling refreshed after recovering well after starting on both days of the New Zealand Cup carnival.
Majestic Man went a big race for fourth in Tough Monarch's free-for-all, before battling into seventh in the Dominion behind Habibi Inta.
The 5yr-old did a power of mid-race work before fighting hard to just miss a top-three spot in the first of his group 1 assignments.
Williamson said he thought the effort was what held Majestic Man back from showing his best in the second of the features.
''It was a big effort on Tuesday and I just don't think he backed up on Friday,'' the trainer said.
''But, he seems to have bounced back pretty well from it ahead of the trip up north.''
Williamson may need to be at his masterful best to help Majestic Man back up for three Interdominion heats in the space of eight days, starting next Friday.
The trotter has three key factors on his side to help him breeze through the first two of those heats.
Racing under mobile conditions, over sprint distances and a right-handed track mean Majestic Man should get perfect circumstances to score maximum qualifying points on nights one and two.
Monty Python is in a contrasting position. The 10yr-old is not completely suited to the early sprint racing, but is expected to thrive under the staying conditions of heat 3 and the series final.
Monty Python heads north after delighting Williamson with his gritty third placing behind Habibi Inta in the second-fastest running of the Dominion.
''We were rapt with him; he just thrives on that pressure racing,'' the trainer said.
''He should get that if he is able to get through to the final, but obviously he is not as suited to the sprint races.''
Despite his proven record in big staying races, Monty Python is rated the outsider of the three horses with whom Williamson is connected.
Majestic Man has been at $21 odds this week to win the trotting series final, Kenny's Dream at $31 and Monty Python at $61 price.
Kenny's Dream will have just her 16th start in next Friday's opening-round heat.
Earlier this week, Spankem was withdrawn from the pacing series after he was diagnosed with a leg injury which will rule him out of racing for summer.
Former Dominion winner Marcoola has joined the stable of master trainer Barry Purdon for the Interdominions while Otago-bred trotter McLovin is now a likely starter, after previously looking doubtful.
